Appendix A lists the differences between Python 2 and 3 that you'll need to know in order to make changes to the source code. These aren't all the differences, but they'll cover the ones you need to know for the programs in the book.

Probably better to begin learning Python 3 at this point, assuming you're using 3.3 or higher, unless you have a specific need to use Python 2. There are some interesting new features, and Python 3 has matured to the point where a lot of libraries are migrating in the near future (within the next year), while the majority of new libraries are targeting Python 3.

Once you have a decent grasp of Python 3, using what you learned to write for Python 2 will be much easier than trying to rewrite Python 3 code while learning.